From CNN Correspondent May Lee
TOKYO (CNN) -- Work crews have begun trying to reach 20 people trapped in a tunnel, after a fourth dynamite blast Wednesday turned a gigantic rock into debris. (1 MB QuickTime movie)
Nineteen people in a commuter bus and one person in a car were trapped Saturday when the rock -- the size of a 20- story building -- slid off a mountain and onto the top of the tunnel. The accident occurred 550 miles north of Tokyo.
Families and friends of the victims, mostly from the nearby fishing village of Furubira, shed tears of relief after the rock collapsed. Among those on the bus are five high school students and three younger children.
"I don't know what to say," cried one man. "Finally, they can start the search. I just don't know what to say."
Rescue workers were using power shovels Wednesday to remove slabs of the rock.
"We want to rescue the people trapped in the tunnel as soon as possible," an official of the Hokkaido Development Agency said. "Although we will continue our work to remove pieces of the slab throughout the night, it now looks impossible to start actual rescue work before early tomorrow morning."
Rescuers spent two days trying to blow up the rock because they feared that immediately digging through the tunnel would trigger another collapse. Three previous blasts chipped away at the rock but not enough so a rescue could begin.
However, it may be days before rescuers reach the victims, all of whom are believed dead. If the search takes much more time, the Hokkaido rescue coordinators may face extreme criticism. They already are being blamed for not reaching the vehicles sooner.
On the day of the avalanche, local officials waited eight hours before calling in Japan's self-defense forces. A similar delay occurred after the Kobe earthquake that caused widespread damage, resulting in a storm of criticism over how Japanese authorities handle crises.
Also Wednesday, Japan's Kyodo News reported that 18 months ago, not far from the avalanche site, another rock twice as big as this one fell from a mountainside. The report suggests that local authorities ignored warning signs of rock instability in the area.
Experts aren't sure what caused the collapse, but they say it may have been due to water seeping into cracks in the mountainside and freezing, forcing fissures to widen over the years and finally loosening the rock.
Search teams had considered other methods to remove the rock, including putting a huge rope around it and dragging it to sea or blasting it with tank artillery or missiles.
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Reuters contributed to this report.
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